1. Field of the Invention
The present invention relates to a light exposure apparatus such as a light exposure apparatus used for manufacturing semiconductors, liquid crystal display elements or the like by means of a photolithographic process, and more particularly to a so-called slit-scanning type light exposure apparatus for successively exposing the pattern of a mask on light-sensitive substrates by scanning the mask and the photosensitive substrates in synchronism in a slit-like illuminating area.
2. Related Background Art
Upon manufacturing semiconductors or liquid crystal display elements by means of a photolithographic process, a projection light exposure apparatus is used which exposes the pattern of photomask or a reticle (hereinafter generally referred to as the "reticle") on substrates (wafers, glass plates or the like) coated with photosensitive material through a projecting optical system. Conventionally, a stepper is mainly used as a projection light exposure apparatus to manufacture semiconductors. The stepper is a projection light exposure apparatus which successively totally transcribes the pattern image of a reticle pattern images in shot areas in a step and repeat way.
However, a so-called slit-scanning type projection light exposure apparatus has come to be developed, which will be described briefly.
In the slit scanning type projection light exposure apparatus, a reticle is scanned at a speed V in a predetermined scanning direction in an illuminating area having an elongated rectangular shape, a circular shape or a hexagonal shape (hereinafter generally referred to as a "slit shape"), wafers are scanned at a speed .beta..multidot.V (where .beta. is the projection magnification of a projection optical system) in a direction conjugate with the scanning direction of the reticle in a light exposure area conjugate with the illuminating area and the projection optical system, and thus pattern images of the reticle is successively exposed and transcribed in exposure fields (shot areas) on the wafers.
The reasons why attention is paid to the slit scanning type light exposure apparatus are as follows:
First, as patterns of semiconductor devices have recently become finer and finer and the size of the devices have become larger and larger, much larger projection optical systems have been required. Thus, the manufacturing cost of the apparatus has become much higher and the size of the apparatus has also become much larger, reducing lowers applicability of the apparatus to manufacture of semiconductors.
Secondly, as the device pattern has been finer and finer, distortions, flatness and astigmatism of the projection image of the projection optical system have come to be very nearly to their limitations, and thus high operational performance required for the stepper cannot be obtained.
With the slit scanning light exposure method, light exposure is performed by the use of only a slit-like light exposure area in the projection optical system of the projection optical system. When, therefore, the same projection optical system is used, the field size of the slit scanning type projection light exposure apparatus can be made larger by 2.sup.1/2 times than that of the stepper. In other words, with the same field size as the stepper, the slit scanning type projection light exposure apparatus can employ an optical system 1/2.sup.1/2 times smaller than the stepper, improving a lens characteristic more than the stepper.
Thirdly, in a case where a reflecting and refracting optical system having a concave reflecting mirror is used as a projection optical system, areas in the light exposure field in which good optical characteristics can be obtained are limited to narrow circular arc portions. Thus, a slit scanning light exposure system is required for exposing the whole pattern of the reticle on wafers.
In the general projection light exposure apparatus, a suitable amount of exposure light (exposure light energy) is selected depending on light sensitivity of photoresists coated on wafers. Under the condition where continuous light is used as exposure light in the stepper, the amount of exposure light is controlled in accordance with the illuminating time length of the exposure light. When pulse light is used, on the other hand, the amount of the exposure light is controlled by the number of pulses of the illuminating light.